Four of the 10 cities with the worst air pollution in the world are in India, a U.N. WHO study shows

NEW DELHI—Four of the 10 cities in the world with the worst air pollution are located in India, a new report showed.

The World Health Organization’s latest study showed that many of the world’s most polluted cities were located in fast-developing nations. The worst levels of small particulate matter were recorded in the eastern Iranian city of Zabol, which is regularly hit by seasonal dust storms, with a so-called PM2.5 reading of 217

That city was followed by Gwalior and Allahabad in India, and Riyadh and Al Jubail in Saudi Arabia. India’s Patna and Raipur were the sixth and seventh most polluted, according to the report by the WHO, .

PM2.5 refers to particulate matter that is smaller than 2.5 micrometers in diameter. The pollutants, which come from dust, soot and smoke, can penetrate deep into the lungs, increasing the risk of heart and lung diseases including asthma and lung cancer, the WHO said.

Delhi, India’s capital, tied with another Indian city, Ludhiana, for 11th worst in the world for air pollution, with a PM2.5 measurement of 122, according to the WHO study. Beijing tied for 36th with a PM2.5 reading of 85. Delhi has recently tested out measures the Chinese capital has used to restrict the number of cars on its roads.